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Research
Tree Rings, Ocean Temperatures, and Megadroughts
by Julio Betancourt, U.S. Geological Survey, and Stephen Gray, Montana
State University
Not long ago, conventional wisdom was that you could not predict the
climate for more than a few days in advance. Then came the awareness of
El Niño and La Niña, and the forecast window increased to
as much as 6 to 9 months, depending on the region and season. A recent
study suggests that opposing shifts in Tropical Pacific and North Atlantic
Ocean temperatures may foretell persistence of disastrous, multiyear droughts
across North America and elsewhere.
Forecasts longer than the 6 to 9 months typical today, if possible, would
rely on two principles: first, the well-defined relationship between temperatures
in the upper 1 meter of the ocean and precipitation on land, and second,
the ocean’s thermal inertia. Once an ocean basin begins to cool
or warm anomalously, it generally tends to stay that way for several years
and even decades. If these slow shifts in ocean regime can be identified
in their early stages, then perhaps they can be used to assess the probability
of disastrous, multiyear droughts across the globe.
In this light, a team of researchers from the U.S. Geological Survey,
University of Wyoming, and Vermont’s Middlebury College analyzed
precipitation changes occurring over decades and recorded in 750-year-old
tree-ring chronologies in the Rocky Mountain states of Colorado, Montana,
Wyoming, Arizona, New Mexico, and Utah. They found that the tree-ring
records exhibited significant oscillations in precipitation that lasted
between 40 and 70 years. In general, multidecadal oscillations in the
tree-ring record are not cyclical and are not always in phase across the
Rockies, suggesting complex linkages between regional precipitation and
ocean temperatures.
Occasionally, these oscillations can synchronize, particularly in times
of “megadroughts” that affect large regions of the country
for a decade or more, such as occurred in the late 1500s and the 1950s.
The 1950s’ drought was associated with a persistently cold Tropical
Pacific Ocean and warm North Atlantic Ocean. Similar conditions have been
in place since 1998, and once again the Rockies, Great Plains, and Southwest
have been stricken by drought. Because no comparable 750-year-long proxy
records exist of sea-surface temperatures in the Tropical Pacific and
North Atlantic, the demonstrated link between ocean temperatures and precipitation
in the Rockies is limited to the last century.
Since climate on these time scales is obviously not cyclical, the next
best hope for long-term drought prediction lies with identifying precursor
states in oceanic climate, similar, in fact, to the way we use Tropical
Atmosphere Ocean moorings to predict and monitor El Niño or La
Niña.
It is hoped that the information on the relationship between sea-surface
temperatures and North American climate will help guide us in more effective
and long-term water management and to anticipate climatic effects on ecosystems.
For example, the current megadrought is playing a major role in resetting
plant demographic clocks across the Rockies through wildfires, insect
outbreaks, and tree mortality from physiological stress. Given the longer
growing season associated with global warming, the species present in
the region now would be more likely to be replaced by other native and
nonnative species, producing long-term vegetation changes.
For more information, contact Julio Betancourt, Paleoecologist, U.S.
Geological Survey and University of Arizona, Desert Laboratory, 1675 W.
Anklam Road, Tucson, Arizona 85745, (520) 670-6821 extension 107, jlbetanc@usgs.gov,
or Stephen Gray, Post-Doctoral Research Associate, Big Sky Institute,
Montana State University, Bozeman, Montana 59717, (406) 994-7023, sgray@montana.edu.
Lots Less Lesser Scaup
by Josh Vest and Richard Kaminski, Mississippi State University
In the 1990s, when snow and rain returned to the prairies and parklands
after a long period of drought, and when conservation programs expanded
upland cover in the U.S. Prairie Pothole Region, most North American waterfowl
breeding populations experienced impressive increases. A few species,
however, did not respond—populations of greater and lesser scaups
continued to decline.
The smaller lesser scaup primarily uses the Mississippi Flyway whereas
the greater scaup uses both the Mississippi and Atlantic Flyways. These
species remain the most abundant diving ducks in North America, but their
populations have been “taking a dive” since the late 1970s.
With an estimated 3.73 million breeding scaup in 2003, the birds are 29%
below their long-term average of 5.28 million. It is the fourth lowest
estimate on record since breeding duck surveys began in 1955.
Because lesser scaup is sought widely by duck hunters in the Mississippi
Flyway, and because it is the most abundant diving duck wintering in Mississippi
and Louisiana, scientists from Mississippi State University (MSU) and
Louisiana State University (LSU) initiated research in 1999 to help solve
the mystery surrounding the bird’s decline.
During falls and winters of 1999 through 2001, the scientists collected
lesser scaup from hunters throughout the Mississippi Flyway to estimate
body weights and internal parasite loads. The birds lost weight during
fall migration and winter, dropping about 23% of their weight as they
migrated from Canada to Louisiana. Both males and females collected from
Mississippi catfish ponds weighed about 60 grams more, on average, than
scaup harvested from traditional wintering habitats along the Louisiana
coast. Additionally, weights generally were greater or similar to estimates
from birds collected at comparable locations in the flyway during the
1980s. This suggests that food and habitat conditions during fall and
winter may not be negatively affecting populations.
Internal parasites were discovered in all scaup sampled. Estimates of
total parasite burdens from this study were similar to estimates from
studies conducted in the mid 1970s on the breeding grounds in Canada,
before scaup populations plummeted. This suggests that parasite burdens
have not increased in recent decades and may not be influencing the declines.
However, scientists caution that recent scaup die-offs in the Great Lakes
Region from trematodes and bacterial infections warrant close monitoring
of the birds and their foods and habitats.
This research suggests that the fall and winter periods of the lesser
scaup’s annual cycle in the Mississippi Flyway may not include the
major factors affecting scaup populations. Interestingly, an ongoing study
at LSU has uncovered evidence that food resources and body condition of
scaup along spring migration routes in the flyway and on the breeding
grounds are significantly less than they were 20 years ago.
Taken together, the MSU and LSU studies are helping to piece together
the puzzle of declining numbers of lesser scaup. Future research will
focus where it is needed most to help sustain this important species.
For more information, contact Richard Kaminski, Professor, Mississippi
State University, Department of Wildlife and Fisheries, Box 9690, Mississippi
State, Mississippi 39762, (662) 325-2623, rkaminski@cfr.msstate.edu.
Lesser Scaup Research Partners
Mississippi State University
Louisiana Cooperative Fish and Wildlife Research Unit
Mississippi Cooperative Fish and Wildlife Research Unit
Delta Waterfowl Foundation
Institute for Wetland and Waterfowl Research
U.S. Fish and Wildlife Service
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